Parent Company Only Condensed Financial Information Condensed Statement of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Interest income	$ 279,232	$ 264,791	$ 253,926	$ 248,816	$ 243,725	$ 229,326	$ 213,841	$ 205,024	$ 1,046,765		$ 891,916		$ 729,621
Interest expense	(10,163)	(10,131)	(10,155)	(9,891)	(8,988)	(8,761)	(8,876)	(8,696)	(40,340)		(35,321)		(32,277)
Gains on derivative instruments, net									83,805		96,845		42,184
Gains on investment securities, net									89,445		267,023		419,408
Impairment loss on SVBIF Sale Transaction									0		(13,934)		0
Income tax expense	(53,697)	(57,017)	(54,974)	(63,066)	(46,077)	(40,207)	(35,928)	(61,296)	(228,754)	[1]	(183,508)	[1]	(146,830)	[1]
Net income available to common stockholders	$ 87,512	$ 81,733	$ 86,143	$ 88,516	$ 57,990	$ 63,977	$ 50,953	$ 90,950	343,904	[1],[2]	263,870	[1]	214,517	[1]
Parent Company
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Interest income									964		2,534		3,545
Interest expense									(34,169)		(21,863)		(24,408)
Dividend income from subsidiary									0		0		10,000
Gains on derivative instruments, net									55,477		66,604		47,421
Gains on investment securities, net									39,447		8,750		15,238
Impairment loss on SVBIF Sale Transaction									0		(9,564)		0
General and administrative expenses									(54,822)		(53,912)		(54,389)
Income tax expense									(14,448)		(15,038)		(15,824)
Loss before net income of subsidiaries									(7,551)		(22,489)		(18,417)
Net income available to common stockholders									343,904		263,870		214,517
Parent Company | Nonbank Subsidiaries
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Loss before net income of subsidiaries									44,591		37,009		58,075
Equity in undistributed net income of subsidiary									44,591		37,009		58,075
Parent Company | Bank Subsidiaries
Schedule of Condensed Consolidating Statement of Operations [Line Items]
Loss before net income of subsidiaries									306,864		249,350		184,859
Equity in undistributed net income of subsidiary									$ 306,864		$ 249,350		$ 174,859

[1] Prior period amounts have been revised to reflect the retrospective application of new accounting guidance adopted in the first quarter of 2015 related to our investments in qualified affordable housing projects (ASU 2014-01). See Note 2— "Summary of Significant Accounting Policies” of the “Notes to the Consolidated Financial Statements” under Part II, Item 8 of this report for additional details.

[2] During the second quarter of 2015 we adopted new accounting guidance related to our consolidated variable interest entities (ASU 2015-02). Amounts prior to January 1, 2015 have not been revised for the adoption of this guidance. See Note 2— "Summary of Significant Accounting Policies” of the “Notes to the Consolidated Financial Statements” under Part II, Item 8 of this report for additional details.